Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.2201b&link_type=abstract
American Astronomical Society Meeting 210, #22.01; Bulletin of the American Astronomical Society, Vol. 39, p.124
Astronomy and Astrophysics
Astronomy
Scientific paper
We perform helioseismic holography on the solar convection simulations of Benson, Stein, and Nordlund and compare the observed acoustic travel-time perturbations with the expected travel times from the horizontal flows in the simulations computed from forward models under the assumption of the Born approximation. The agreement between the observed and model travel times reinforces the validity of helioseismic holography in the detection of subsurface horizontal flows. However, from the variation of the signal-to-noise ratio with depth, we conclude that the local helioseismic detection of individual supergranule-size (or smaller) flow patterns is not possible for depths below about 5 Mm below the surface over time scales less than a day. We suggest that similar limitations exist regarding the detection of analogous subsurface flows in the Sun. We also study the depth dependence of the contribution to the travel-time perturbations for the simulated flows. For holography measurements focused down to 7 Mm, we find that approximately half of the observed signal originates within the first 2 Mm below the surface. A consequence of this is a a rapid decrease (and possible reversal) of the travel-time perturbations with increasing focus depth due to the contribution to the measurements of oppositely directed surface flows in neighboring convective cells. This confirms an earlier interpretation of similar effects reported from holographic analyses of observations of supergranulation.
This work is supported by NASA contracts NNH05CC76C and NNH04CC05C, NSF grant AST-0406225 , and a subcontract through the HMI project at Stanford University awarded to NWRA, and by NASA grant NNG04GB92G and NSF grant AST-0605738 to MSU.
Benson Dave
Birch Aaron C.
Braun Douglas
Nordlund Aake
Stein Robert F.
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